Summary: Animal models are used for the evaluation of the safety and immunogenicity of acellular pertussis vaccines before administration to humans. The aerosol challenge model provides a reproducible system for the study of virulence factors and immunity involved in respiratory infection and subsequent disease. Clinical studies have shown that acellular pertussis antigens are protective against disease; however, to date, there is no laboratory correlate of vaccine mediated protection. In some recent publications, authors have suggested that when mice were immunized with DTP vaccines [with either whole-cell or acellular pertussis component] and then challenged with an aerosol or intranasal B. pertussis, the clearance of infection from the lungs paralleled the ability of these vaccines to protect children against pertussis. In previous studies in our laboratory, this aerosol model, despite very good intra- and inter-assay reproducibility, was not able to distinguish vaccines of high and low clinical efficacy. FY2001 activities: Previously, our laboratory participated in an international, multi-center collaborative study that evaluated three basic protection mouse models [intranasal, intracerebral, and aerosol] for the assay of vaccines containing an acellular pertussis component. In FY2001, we participated in the review and evaluation of the previous study and in the planning of a follow-up study now in-progress. In the follow-up study, participating laboratories will evaluate vaccines of varying potency using a common mouse model.